Silicon single crystals in thin sheet form are desirable for several important reasons. They achieve materials savings in silicon utilization and provide product use possibilities in photovoltaic (solar cell) installations. They also offer a very low cost potential of making semiconductor ribbon by continuous process means for subsequent device fabrication.
Several investigators have explored various methods of growing single crystalline silicon sheet. Some of the known art for the purpose is revealed, amongst other sources, in: an article by J. V. Stepanov in Soviet Physics -- Technical Physics, 29, 339 (1959); an article by J. C. Swartz, T. Surek and B. Chalmess in J. Electronic Materials, 4, 255 (1975); a report dated Dec. 15, 1975 prepared by G. H. Schmuttke et al entitled "SILICON RIBBON GROWTH BY A CAPILLARY ACTION SHAPING TECHNIQUE" identified as Quarterly Technical Progress Report No. 2 under JPL Contract No.: 954144 (a Subcontract under NASA Contract NAS7-100 - Task Order No. RD-152); and a presentation of J. A. Fautendyk at the "International Solar Energy Society Conference `Sharing The Sun`" made Aug. 16 - 20, 1976 at Winnepeg, Manitoba, Canada and entitled "DEVELOPMENT OF LOW-COST SILICON CRYSTAL GROWTH TECHNIQUES FOR TERRESTRIAL PHOTOVOLTAIC SOLAR ENERGY CONVERSION". U.S. Pat. Nos. 3,393,054; 3,591,348; and 3,617,223 also pertain to this technology. So does the present Applicants' copending U.S. Patent Application entitled "APPARATUS FOR THE PRODUCTION OF RIBBON SHAPED CRYSTALS", Ser. No. 680,072, filed Apr. 26, 1976.
Three of the more widely employed procedures for single crystalline silicon sheet growth are known as: (i) the "Stepanov Technique"; (ii) the "Inverted Stepanov Technique"; and (iii) "Edge-Defined Film-Fed Growth" (i.e., "EFG"); plus various modifications thereof (and not excluding the more conventional Czochralski silicon crystal growth method). One of the essential differences between the first three of the specified procedures lies in the contact angle (.phi.) between the molten silicon and the die material. For EFG, .phi. should be much smaller than 90.degree.. On the other hand, .phi. should be larger than 90.degree. in the Stepanov Technique, while it can be more or less than 90.degree. in the Inverted Stepanov Technique.
Molten and near molten (e.g., solidifying from the melt) silicon is extremely and unusually reactive. It tends (even at temperatures as low as 100.degree. C. or so below its melting point to those where it may actually be vaporized) to attack or corrode and/or become undesirably contaminated by practically all of the die and crucible materials that have been employed for growing single crystalline silicon sheet. This, obviously, is very disadvantageous.
The present invention, quite benefically, provides a greatly improved material of construction for die and/or crucible components in silicon crystal growth operations and for handling molten silicon through its solidification therein.